The genetic effects of asbestos on cultured cells were studied in order to correlate them to asbestos carcinogenicity. This is achieved by the investigation of cytotoxicity effects chromosomal aberrations, phagocytosis and induced gene mutations by the crystals. The occurrence of pleural and peritoneal mesotheliomas and carcinomas in the gastro-intestinal tract is linked with the inhalation of asbestos fibres. Experimentally, mesotheliomata have been induced by the intrapleural inoculation of fibres into rats. Experiments also showed that very large amounts of asbestos dust could be taken up by individual lung macrophages and remain in macrophage-converted fibroblasts. These findings suggest that the incorporation of the fibres disturbs processes at the cellular level.